Heat treating furnace with walking beam drive

ABSTRACT

A furnace construction for the heat treating of metal materials and including a conveying apparatus that provides for step-bystep movement of the metal materials through the heat treating chamber of the furnace construction, the drive for the conveying apparatus comprising a walking beam assembly. Sintering of various kinds of materials including metal compacts may be accomplished by the furnace construction and since treatment of the materials at relatively high temperatures is necessary during the heat treating cycle, a special sealing structure is provided for preventing contamination of the high temperature zone during sintering of the materials and the cooling thereof after the sintering cycle.

United States Patent Westeren et al.

[ s] 3,656,720 [451 Apr. 18, 1972 [54] HEAT TREATING FURNACE WITH WALKING BEAM DRIVE [73] Assignee: C. I. Hayes Inc., Cranston, RI.

[221 Filed: Mar. 16, 1970 [21] App]. No.: 19,709

FOREIGN PATENTS OR APPLICATIONS 1,161,276 8/1969 Great Britain ..263/6 A 1,325,350 3/1963 France..... ....263/6 A 1,542,339 9/1968 France ..263/6 A Primary Examiner-Charles J. Myhre Attorney-Salter & Michaelson [57] ABSTRACT A furnace construction for the heat treating of metal materials and including a conveying apparatus that provides for step-bystep movement of the metal materials through the heat treating chamber of the furnace construction, the drive for the conveying apparatus comprising a walking beam assembly. Sintering of various kinds of materials including metal compacts may be accomplished by the furnace construction and since treatment of the materials at relatively high temperatures is necessary during the heat treating cycle, a special sealing structure is provided for preventing contamination of the high temperature zone during sintering of the materials and the cooling thereof after the sintering cycle.

7 Claims, 11 Drawing Figures mmmmmmz 7 3,656,720 SHEET 20F 5 INVENTORS HERBERT w. wEsTEREN ERNEST c. GRONQU|ST,JR. MARVIN J. OTT JR. DONALD E. GUN'THER F G 4. BY t ATTORNEYS 8 I PATENTEDAPR] 1912 SHEET m 5 3 656 720 INVENTORS HERBERT w, wEsTEREN ERNEST c. eRqNoulsnaR.

MARVIN J. OT JR. DONALD E. GUNTHER ATTORNEYS PATENTEDAPR 181972 3, 656, 720 sum 5 or 5 F l G. 9

INVENTORS HERBERT. W.. WESTEREN ERNEST C. GRONQU|ST,JR.

VIN TT J MAR J. o R. DO ALD E. GUNTHER BY 2 ATTORNEYS HEAT TREATING FURNACE WITH WALKING BEAM DRIVE BACKGROUND OF THE INVENTION The present invention relates to the heat treating of metallic materials and has particular application in the sintering of carbon steel parts, the metal parts being moved step-by-step but continuously through a pre-heat zone, a high temperature sintering zone and a cooling zone.

Prior to the instant invention, sintering of powdered metal parts was usually accomplished by first preheating the parts in a furnace wherein binders or lubricants impregnated in the parts were burned off during the preheating cycle. The parts were then introduced into a heating zone where they were heated in a controlled atmosphere so as to accomplish the sintering operation. Cooling was then carried out in the usual manner. Continuous belt-type conveyor furnaces for sintering at high temperature levels have been relatively unknown prior to the instant invention, since the conventional type belt conveyor was constructed of materials that were not able to withstand the high temperatures required during the sintering operation. Some prior known furnaces that have been used for sintering steel parts at high temperatures have employed metal trays in which the work load was received, the trays being positioned in end-to-end relation and advanced through the furnace by manually pushing the trays at periodic intervals. However, such prior known constructions were difficult to handle and oftentimes the trays became jammed during the sliding movement thereof within the furnace. Roller hearth furnaces have also been used in sintering furnaces, but this kind of conveying mechanism required complicated gland structures and effective water cooling, which structure prohibitively increased the overall cost of the operation of the furnace.

SUMMARY OF THE INVENTION The present invention relates to a furnace construction having a heating chamber located therein through which metallic materials are adapted to be continuously moved for the heat treatment thereof. In order to avoid the use of conventional belting as used with prior known conveyors for heat treating furnaces, a walking beam type of conveying assembly is employed herein and includes a movable bed that is engageable .with work holders for transferring the work holders through the heating chamber in a step-by-step motion. Since the heating chamber is operable at relatively high temperatures, it is necessary to seal the supports that interconnect the walking beam assembly to the movable bed thereof that is located within the heating chamber; and for this purpose a unique bellows-type seal construction is employed.

The furnace construction as embodied herein has particular application in the heat treating of various articles and in the sintering of various materials, and for this purpose includes a pre-heat chamber that is located upstream of a high temperature chamber in which the materials are sintered. A unique heating element and support therefore are incorporated in the pre-heat unit and provide for the pre-heat temperatures as required. The pre-heat and sintering units are employed in combination with a cooling unit that is located downstream of the sintering chamber, the walking beam assembly further providing for movement of parts through the cooling unit in step-by-step relation. Since sintering is contemplated in the use of the furnace construction as embodied herein, a controlled atmosphere is circulated through the units and the flow of atmosphere is arranged so that proper protection for the metal parts and furnace interiors is maintained.

Accordingly it is an object of the present invention to provide a furnace construction having a walking beam drive for continuously transferring metal parts through a heating chamber of the furnace during the heat treatment thereof.

Another object of the invention is to provide a furnace having a walking beam drive for moving articles to be heat treated therethrough, the support columns that interconnect the walking beam drive to the movable bed that is located in the heating chamber, being efiectively sealed by bellows-type seal units.

Still another object is to provide a furnace construction for sintering carbon steel parts that includes a pre-heat or bumofi zone, a heat treating or sintering zone and a cooling zone, the carbon steel parts being transferred through the zones by a walking beam drive which incorporates a movable bed that cooperates with a fixed bed in the units to move the carbon steel parts in step-by-step relation therethrough.

Still another object is to provide a unique heating element and support therefore for use in the pre-heat zone of the furnace construction embodied herein.

Still another object is to provide a pre-heat or bumoff zone in a sintering furnace that includes a muffle having a special configuration that provides for operation of a walking beam drive for transferring metal parts through the muffle'.

Still another object is to provide a bellows-type seal construction for use with a supporting column of a walking beam drive, the seal construction sealing the interior of the furnace heating chamber during operation of the walking beam drive.

Other objects, features and advantages of the invention shall become apparent as the description thereof proceeds when considered in connection with the accompanying illustrative drawings.

DESCRIPTION OF THE DRAWINGS FIG. 1 a is a vertical sectional view of a portion of the furnace construction embodied in the present invention showing the pre-heat zone, the forward section of the sintering zone and the walking beam drive that transfers the article to be heat treated through the various zones;

FIG. 1 b is a vertical sectional view that is a continuation of FIG. I a and shows the rear section of the sintering zone; and the cooling zone that is located downstream of the sintering zone;

FIG. 2 is a vertical sectional view taken along line 2-2 in FIG. 1 a;

FIG. 3 is a vertical sectional view taken along line 3-3 in FIG. 1 a;

FIG. 4 is a vertical sectional view taken along line FIG. 44 in FIG. 1 b;

FIG. 5 is a partial perspective view of the forward portion of the pre-heat or bumoff zone illustrating the interconnection of the walking beam drive to the transfer device that extends through the pre-heat zone;

FIG. 6 is a side elevational view with parts shown in section of the forward portion of the furnace construction showing the walking beam drive unit and the position thereof where the walking beams are elevated;

FIG. 7 is a view similar to FIG. 6 showing the position of the walking beam assembly when the walking beams are shifted longitudinally forwardly;

FIG. 8 is a view similar to FIGS. 6 and 7 showing the position of the walking beam assembly when the beams are moved vertically downwardly;

FIG. 9 is an elevated view showing a modified form of the walking beam assembly; and

FIG. 10 is a perspective view with parts broken away and shown in section of a heating element and support tile therefore as employed in the pre-heat zone of the furnace construction embodied herein.

DESCRIPTION OF THE INVENTION Referring now to the drawings and particularly to FIGS. 1 a and l b, the furnace construction embodied in the present invention is generally indicated at 10 and as shown includes apparatus that has particular application in the heat treating of powdered metal materials for sintering. As will be described hereinafter, various components of the furnace construction are suitable and are applicable for use in the heat treating of materials other than for sintering, but for purposes of this description, reference will be made to the sintering of carbon steel parts.

Referring again to FIG. 1 a and 1 b, the furnace construction as illustrated is defined by a bumoff or pre-heat unit generally indicated at 12. Located downstream of the pre-heat unit 12 is a sintering unit generally indicated at 14, while downstream of the sintering unit 14 is a cooling unit generally indicated at l6.'As will be described, the metal parts to be sintered are movable through the heating chambers of the preheat and sintering units and through the cooling unit 16 in an intermittent or step-by-step motion and for this purpose a walking beam drive generally indicated at 18 is provided. The walking beam drive 18 is uniquely constructed and arranged for transfer of the articles through the furnace heating chambers and cooling unit without the requirement of additional I feed mechanism or push bars, and in this connection includes a walking beam assembly that provides for continuous stepby-step feed of the articles through the furnace units.

' As illustrated in FIG. 1 a, the burnoff or pre-heat unit 12 includes a housing 20 having refractory insulation material located therein as indicated at 21, the housing 20 being supported by vertical standards 22 and 24 located at the forward and rearmost ends thereof. Formed in the housing 20 is a heating chamber 26 that communicates with the forward end of the housing 20 through an inlet opening 28 and with the rear end of the housing 20 through a discharge opening 30. As will be described the bumoff unit provides for liberating binders and lubricants from the compacted metal parts to be sintered and in this connection, temperatures within the heating chamber 26 may only reach 800-900 F. Since this temperature is relatively low, a metallic muffle 32 can be used in the heating chamber and this prevents zinc stearates or equivalent gases that are liberated from the carbon steel parts from coming in contact with a source of the heat such as heating elements 33 that are located within the heating chamber 26. Since the metal parts to be sintered must be moved through he metallic muffle 32, it is uniquely constructed for use with the walking beam assembly and as illustrated in FIG. 2 is defined by an upper wall 34, side walls 36 and 38, and a lower wall construction including spaced end portions 40 and 42, downwardly projecting portions 44 and 46 and a central bed portion 48 located between the portions 44 and 46. As will be described, the portions 44 and 46 define pockets that receive elongated bars 49 and 50 respectively therein, the bars 49 and 50 cooperating with the walking beam assembly to continuously move a work load through the muffle 32 in step-by-step relation.

The pockets defined by the portions 44 and 46 in the muffle 32 are mounted on a plurality of transverse bars 52 that are located adjacent to the bottom of the heating chamber 26. Fixed below the transverse bars 52 and also mounted at the upper end of the heating chamber 26 are a plurality of transversely extending refractory heating element support members, one of which is generally indicated at 54 in FIG. 10. The refactory support members 54 are especially designed to support pairs of the sinuously formed heating elements 33 and for this purpose are provided with a body portion 58 to which side walls 60 and 62 are joined. Formed as an integral part of the side walls 60 and 62 are inwardly extending flanges 64 and 66, respectively. Located intermediate the side walls 60 and 62 is a central rib 67 that is formed in a T" configuration, and includes outwardly extending flanges 68 and 69; the flanges 68 and 69 and the central rib 67 cooperate with the flanges 64 and 66 to define channels for receiving the sinuously formed heating elements 33 therein. The refractory supports 54 as illustrated in FIG. 1 a are located at the bottommost end of the heating chamber 26 of the pre-heat unit 12 in that. position shown in FIG. 10, and are also mounted atthe upper end of the heating chamber 26 in reverse position, wherein the heating elements 33 are captured within the channels and are supported on the flanges 68 and 69 of the central rib 67 and the flanges 64 and 66 joined to the side walls 60 and 62 respectively.

In order to provide for proper purging of the liberated binders or lubricants that are burned off during the pre-heat cycle in the treatment of the metal parts to be sintered, a flow of exothermic gas having approximately 6 percent carbon monox-- ide is introduced under pressure into the muffle 32 at the discharge end thereof, as indicated at 56. The exothermic gas as introduced into the muflle 32 flows in a direction that is counter-current to the movement of the'work load through the muffle 32 and the purged materials and gas exit from the chamber 26 through the entrance end of the mufile 32 where they are burned in atmosphere and'vented in any conventional manner. It is understood that the flow of the exothermic gas is of sufficient quantity to absorb all of the liberated hydro carbons, thereby preventing conversion and breakdown of solids within the muffle, and thereby maintaining a relatively clean condition therein. The medium rich exothermic purge gas also protects the parts from oxidizing or decarborizing at the preheat temperature, which is maintained at approximately 850 F.

Referring again to FIGS. 1 a and l b the sintering unit 14 is show including a housing 70 that is located in spaced relation downstream of the housing 20 of the pre-heat unit 12. The housing 70 is suitably supported on vertical standards 72 and 74, which as illustrated in FIG. 3 are mounted on base members 75 and 76 that extend longitudinally of the furnace construction. Suitable cross bars 77 located at the upper end of the housing 70 are interconnected to the standards 72 and 74 and cooperate to fix the housing 70 in position. An inlet duct 78 communicates with the discharge end of the muffle 32 and extends inwardly of the housing 70 for communication with a heating chamber 80 formed therein. As illustrated in FIG. 3, the interior of the housing 70 is provided with layers of refractory material indicated at 82 which are assembled in any convenient manner to define the heating chamber 80 centrally thereof. Forming the bed of the heating chamber 80 and fixed therein are a plurality of spaced refractory plates 84 and 86 between which movable plates 88 are located, the movable plates 88 defining a movable bed and being secured to movable hearth supports 90. The movable hearth supports 90 are formed in stepped relation along the sides thereof and are supported by grids 92, that are interconnected to the walking beam assembly for intermittent or step-by-step movement therewith as will be described. As further shown in FIG. 3 the refractory tiles of the furnace housing 70 are stepped to accommodate the hearth supports 90 therebetween.

Extending transversely of the heating chamber 80 are a plurality of rod-like heating elements 94 that extend through the refractory material of the housing 70 and outwardly of the housing side walls for connection with terminals 96 of conventional construction. Suitable gasket assemblies generally indicated at 98 seal the openings in the walls of the housing 72 through which the heating elements 94 extend. It is understood that current from a source is supplied to the terminals for energizing the heating elements 94, the heating elements 94 being of the Globar" type that are capable of producing temperatures in the heating chamber 80 as high as 2,400 F. It is also contemplated to use a heating element and holder therefor in the sintering unit 14 that is similar in construction to the heating element 33 and support 54 described above, except that the material in the element would be molybdenum. Such a heating element would be capable of end standards 104 and 105 cooperate with the standards 72 and 74 for mounting the housing of the cooling unit in place. Across bar 106 interconnects the standards 104 and 105 at the end of the cooling unit and adds additional support to the construction. Located at the discharge end of the cooling'unit 16 is a discharge zone 107 in which vertically staggered curtains 108 are located that provide for discharge of the heat treated articles exteriorly of the cooling unit 16 without unduly exposing the interior of the housing sections 100 and 102. An endothermic gas or equivalent atmosphere thereof is introduced into the section 100 of the cooling unit 16 through a gas inlet 112, the endothermic gas or atmosphere flowing both in the direction of the sintering unit 14 and the discharge end of the cooling unit 16. It is seen that gas as so introduced through the inlet 112 produces a condition within the cooling unit that is compatible with the carbon content of the metal parts passing through, thereby providing a protective atmosphere for the metal parts.

As illustrated in FIG. 4, the housing 100 of this cooling unit is formed with an inner wall 114 that cooperates with the outer wall to define a cooling space 116 therebetween through which a cooling liquid is circulated. Both the inner and outer walls of the housings 100 and 101 have reduced bottom portions, the inner wall 1 l4 defining a channel for receiving a plurality of movable sections 118. Each section 118 is supported by a column 120 that is interconnected to the walking beam assembly as will be described hereinafter. As further illustrated in FIG. 4, the configuration of the housing walls in the cooling unit 16 define spaced fixed beds 121 and 122 on which the work load is received as it is passed through the cooling zone in step-by-step relation by the walking beam drive.

In order to move a work load through the pre-heat, sintering and cooling units, the walking beam drive 18 is provided and as illustrated in FIG. 3, include spaced beams 123 and 124 that are interconnected to the movable segments in the units and are further interconnected to operating cylinders 125 and 126, the cylinders being operable in pre-determined timed relation to produce a rectangular movement of the beams. The beams 123 and 124 are fixed at the head ends thereof to spaced plates 127 and 129, which as illustrated in FIG. 5 are joined to the elongated bars 49 and 50 through brackets 130. The beams 123 and 124 are also fixed to a pivot connection 131 to which a piston rod 132 of the cylinder 125 is pivotally connected, the opposite end of the cylinder 125 being pivotally mounted on a fixed bracket 134 through a pivot connection 135. The cylinder 126 is pivotally connected to the beams 123 and 124 through a pivot connection 136 and a bracket 138. Formed as an extension of the piston rod of the cylinder 126 is a tie rod 140, the tie rod 140 being operable by the cylinder 126 and extending substantially the length of the furnace construction in parallel relation to the walking beams 123 and 124. In order to support the beams 123 and 124 during the rectangular movement thereof, a plurality of links 142 that are received on bearing blocks 146 mounted on the base members 75 and 76. As seen in FIGS. 1 a and 1 b the links 142 are spaced along the length of the walking beams 123 and 124 on both sides thereof.

In operation of the walking beam drive 18, a step-by-step motion is required that will transfer the work load through the pre-heat, sintering and cooling units. As is conventional in walking beam drives, the beams as represented at 123 and 124 must be elevated, transferred forwardly, lowered and then transferred rearwardly, this motion effecting a rectangular movement of the walking beams and acting to periodically elevate a work load for transferring it in step-by-step movement along the fixed beds of the pre-heat, sintering and cooling units. Referring to FIGS. 1 a, 6, 7, and 8, the sequential movement of the walking beam assembly is illustrated and it is first assumed that the beams 123 and 124 are disposed in the position as illustrated in FIG. 1 a. In order to elevate the beams in the first movement of the assembly to the position illustrated in FIG. 6, the cylinder 126 is retracted while the cylinder 125 is held in fixed position. Beams 123 and 124 are forced upwardly and the bars 48, 50, hearth supports 88 and sections 118 on which the work load is mounted are moved upwardly approximately one-half inch in the pre-heat sintering and cooling units respectively. In order to accomplish the forward movement of the work load (FIG. 7), cylinder 125 is retracted while cylinder 126 is retained in a fixed position. This produces a forward motion of the beams and the bars 48, 50, hearth supports 88 and sections 118 interconnected to the beams thereby transferring the work load therewith. Downward movement of the beams is accomplished (FIG. 8) by extending the cylinder 125 while the cylinder 126 is held in fixed position. The beams now move downwardly'to locate the work load on the fixed sections of the hearths in the pre-heat sintering and cooling units. The return movement of the beams to the position illustrated in FIG. 1 a is accomplished by extending cylinder 125 and holding the cylinder in the fixed position. It is seen that the work load as carried by the movable portions of the walking beam assembly intermittently moves through the pre-heat sintering and cooling units and as the cylinders 125 and 126 are periodically operated in timed sequence, the work load is lifted by the movable portions within the units, shifted forwardly and then moved downwardly on the fixed bed portions as the beam drive recycles.

Since the temperatures in the heating chamber 26 of the preheat unit 12 only reach approximately 800 to 900 F. for purposes of burning off the binders and lubricants of the powdered metal parts processed therethrough the muffle 32 is used, and in this connection, it is specifically formed for receiving the bars 49 and 50 that act to transfer the work load through the pre-heat unit. It is not practical to extend the bars 49 and 50 through the sintering and cooling units and this movement of the hearth segments 90 and segments 118 is accomplished through columns or rods that project through the bottom walls of the housings 20 and 70. Sealing of the heating chamber of the sintering unit zone 14 of of extreme importance, since this chamber has a treatment atmosphere circulating therethrough and must be protected from out side atmosphere during the sintering operation of the metal parts passing therethrough. As illustrated in FIG. 3, the bottom end of the housing 20 through which the connection of the walking beam assembly extends for engagement with the hearth segment is effectively sealed by a bellows-type seal. As previously mentioned, the hearth segment 90 is carried by a grid 92 on the corners of which elements 150 are located. The elements 150 are recessed on the underside thereof to receive support rods 152 the bottommost ends of the rods 152 being threaded for receiving threaded bolts 154 therein. The threaded bolts extend through cross members 156 welded to the beams 123 and 124, and therefore as the beams 123 and 124 are moved in the manner as described above, the support rods 152 will move therewith to transport the hearth segments 90 and movable bed supports 88 therewith.

In order to effectively seal the rods 152 as they extend through the bottom of the housing 70, bellows-type seals 158 are provided. The seals 158 envelope the support rods 152 and are secured at one end to the bottommost end of the housing 70 and at the other end to plates 160 that are secured to spacer tubes 162. As illustrated in FIG. 3, the spacer tubes 162 are fixed to the cross bars 156 and are also movable therewith. It is seen that the bellows seals 158 envelope the support rods 152 and thereby effectively seal the interior of the heating chamber 80.

The interior of the housing 112 of this cooling unit 14 is also effectively sealed from outside atmosphere by a bellows-type seal 164 as illustrated in FIG. 4. The bellows seal 164 envelopes the support column 120 and is secured to a flange 166 that mates with a similar flange joined to the bottommost end of the jacket housing 1 10. The lower end of the bellows 164 is fixed to a flange 168-that is mounted on a tubular member 170, the tubular member being fixed to a U-support 172. Extending through the upper wall of the U-support 172 is a bolt 174 that also projects through the flange 168 and engages the lowermost end of the support column 120. Since the U-support 172 is secured to a cross member 174 that is joined to the walking beam 123, 124, by support arms 176, the support rod 120 is effectively interconnected to the walking beam assembly. It is understood that as the walking beams are moved in the rectalinear motion by the cylinders 125 and 126, the support rod 120 will move therewith, thereby carrying the movable segment 118 therewith. The work as mounted on the movable segment 118 will be transferred therewith and carried step-by-step through the cooling unit 14. It is seen that the bellows seal 164 effectively seals the interior of the cooling unit 16 and prevents the housings thereof from being contaminated by outside atmosphere.

Referring now to FIG. 9 a modified form of the walking beam assembly is illustrated and is generally indicated at 180. The operation of the walking beam assembly 180 is generally the same as that described in connection with FIGS. 1 a, 6, 7, and 8 and includes a cylinder 182 that is fixed to a tie rod 184 located above the walking beams and pivotally interconnected to the beams through a pivot connection 186 joined to a vertical support 187. The other cylinder indicated at 188 is located below the beams and is fixed to a bracket 190 through a pivot connection 192. A piston rod 194 extends from the cylinder 188 for connection to the vertical support 187 of the beam assembly. A plurality of levers 196 join the tie rod 184 to the walking beams through the pivot connections 198. Rollers 200 locatedat the bottommost end of the levers 196 are received on bearing supports 202. The modified form of the walking beam assembly illustrated in FIG. 9 is operative in the same manner as described above to transfer the work load through the pre-heat, sintering and cooling units.

It is seen that the furnace construction as described herein, is effective to continuously preheat an article for the purging of liberated binders or lubricants in the pre-heat chamber, whereafter the article is transferred to a sintering unit by the walking beam drive and is heat treated to produce effective sintering thereof. Cooling is accomplished in the manner as previously described.

Although not specifically described herein, it is understood the walking beam drive assembly and/or the sealing assembly for use therewith may be incorporated in a vacuum type furnace wherein the heating chamber is operated at sub-atmospheric pressures; or in a furnace wherein the heating chamber is operated at pressures greater than atmospheric.

What is claimed is:

l. A furnace construction comprising a housing, a heating chamber located in said housing, means for heating said heat- 'ing chamber to an elevated temperature, and means for conveying a work load through said heating chamber in step-bystep relation, a stationary bed extending through said heating chamber for receiving said work load thereon, said conveying means including a movable bed located adjacent to the stationary bed, an elongated beam assembly located below said movable bed exteriorly of said heating chamber, means for interconnecting said beam assembly to said movable bed, means for sealing said interconnecting means so as to protect the interior of said heating chamber, means interconnected to said beam assembly for intermittently driving said beam assembly to produce a step-by-step movement of said work load on said stationary bed thereby advancing said work load through said heating chamber, said means interconnecting said beam assembly to said movable bed including a plurality of connecting members that are secured to said beam assembly, a refractory structure carried by said connecting members and movable therewith together with said beam assembly, said movable bed being joined to said refractory structure and movable therewith, said sealing-means including bellows members that surround said connecting members and seal openings in said housing through which said connecting members extend, said bellows members being further sealed to said beam assembly and movable therewith in the step-by-step movement of said movable bed, and a grid of refractory material interposed between the refractory structure on which said movable bed is carried and said connecting members, said grid defining a supporting structure for said refractory structure and bed as carried by said connecting members.

2. furnace construction comprising a housing, a heating chamber located in said housing, means for heating said heating chamber to an elevated temperature, and means for conveying a work load through said heating chamber in step-bystep relation, a stationary bed extending through said heating chamber for receiving said work load thereon, said conveying means including a movable bed located adjacent to the stationary bed, an elongated beam assembly located below said movable bed exteriorly of said heating chamber, means for interconnecting said beam assembly to said movable bed, means for sealing said interconnecting means so as to protect the interior of said heating chamber and means interconnected to said beam assembly for intermittently driving said beam assembly to produce a step-by-step movement of said work load on said stationary bed thereby advancing said work load through said heating chamber, said means interconnecting said beam assembly to said movable bed including a plurality of vertical support members, said sealing means including bellows members that envelope said vertical support members for sealing openings in the housing through which said vertical support members extend, said bellows members being sealed to said beam assembly and movable therewith in the step-bystep movement of said movable bed.

3. A furnace construction as set forth in claim 2, an atmosphere being introduced into said heating chamber during the operation thereof, said bellows members providing an effective seal around said vertical support members to prevent contamination of said atmosphere and escape thereof from the heating chamber through the sealing means.

4. A fumace construction as set forth in claim 2, a refractory structure mounted on said vertical support members at the upper end thereof, a refractory inner lining for said heating chamber, said heating means including electrical heating elements that extend transversely through said inner lining in said heating chamber in horizontal spaced relation, said movable bed being mounted on said refractory structure.

5. A furnace construction as set forth in claim 4, said vertical support members being arranged in spaced pairs and extending upwardly and inwardly of the fumacehousing and a grid mounted on the uppermost end of said vertical support members for supporting said refractory structure and movable bed that is mounted thereon.

6. A furnace construction as set forth in claim 2, said interconnecting means further including a refractory structure that is mounted on said vertical support members and supporting said bed, said refractory structure being formed in stepped relation and being received in a stepped portion of a refractory lining formed in said furnace.

7. A furnace construction as set forth in claim 2, said vertical support members being fixed to cross members that are interconnected to said beam assembly, the upper ends of said vertical support members extending into a portion of said housing, and said bellows members being interconnected to said cross members for movement therewith, and being sufficiently flexible to permit movement of said vertical support members located therein, wherein the step-by-step movement of said bed is produced to advance the work load through said heating chamber. 

1. A furnace construction comprising a housing, a heating chamber located in said housing, means for heating said heating chamber to an elevated temperature, and means for conveying a work load through said heating chamber in step-by-step relation, a stationary bed extending through said heating chamber for receiving said work load thereon, said conveying means including a movable bed located adjacent to the stationary bed, an elongated beam assembly located below said movable bed exteriorly of said heating chamber, means for interconnecting said beam assembly to said movable bed, means for sealing said interconnecting means so as to protect the interior of said heating chamber, means interconnected to said beam assembly for intermittently driving said beam assembly to produce a step-bystep movement of said work load on said stationary bed thereby advancing said work load through said heating chamber, said means interconnecting said beam assembly to said movable bed including a plurality of connecting members that are secured to said beam assembly, a refractory structure carried by said connecting members and movable therewith together with said beam assembly, said movable bed being joined to said refractory structure and movable therewith, said sealing means including bellows members that surround said connecting members and seal openings in said housing through which said connecting members extend, said bellows members being further sealed to said beam assembly and movable therewith in the step-by-step movement of said movable bed, and a grid of refractory material interposed between the refractory structure on which said movable bed is carried and said connecting members, said grid defining a supporting structure for said refractory structure and bed as carried by said connecting members.
 2. A furnace construction comprising a housing, a heating chamber located in said housing, means for heating said heating chamber to an elevated temperature, and means for conveying a work load through said heating chamber in step-by-step relation, a stationary bed extending through said heating chamber for receiving said work load thereon, said conveying means including a movable bed located adjacent to the stationary bed, an elongated beam assembly located below said movable bed exteriorly of said heating chamber, means for interconnecting said beam assembly to said movable bed, means for sealing said interconnecting means so as to protect the interior of said heating chamber and means interconnected to said beam assembly for intermittently driving said beam assembly to produce a step-by-step movement of said work load on said stationary bed thereby advancing said work load through said heating chamber, said means interconnecting said beam assembly to said movable bed including a plurality of vertical support members, said sealing means including bellows members that envelope said vertical support members for sealing openings in the housing through which said vertical support members extend, said bellows members being sealed to said beam assembLy and movable therewith in the step-by-step movement of said movable bed.
 3. A furnace construction as set forth in claim 2, an atmosphere being introduced into said heating chamber during the operation thereof, said bellows members providing an effective seal around said vertical support members to prevent contamination of said atmosphere and escape thereof from the heating chamber through the sealing means.
 4. A furnace construction as set forth in claim 2, a refractory structure mounted on said vertical support members at the upper end thereof, a refractory inner lining for said heating chamber, said heating means including electrical heating elements that extend transversely through said inner lining in said heating chamber in horizontal spaced relation, said movable bed being mounted on said refractory structure.
 5. A furnace construction as set forth in claim 4, said vertical support members being arranged in spaced pairs and extending upwardly and inwardly of the furnace housing and a grid mounted on the uppermost end of said vertical support members for supporting said refractory structure and movable bed that is mounted thereon.
 6. A furnace construction as set forth in claim 2, said interconnecting means further including a refractory structure that is mounted on said vertical support members and supporting said bed, said refractory structure being formed in stepped relation and being received in a stepped portion of a refractory lining formed in said furnace.
 7. A furnace construction as set forth in claim 2, said vertical support members being fixed to cross members that are interconnected to said beam assembly, the upper ends of said vertical support members extending into a portion of said housing, and said bellows members being interconnected to said cross members for movement therewith, and being sufficiently flexible to permit movement of said vertical support members located therein, wherein the step-by-step movement of said bed is produced to advance the work load through said heating chamber. 